Is π-Single Bonding (C–π–C) Possible? A Challenge in Organic Chemistry

Abstract

Rikuo Akisaka received his Bachelor's degree in 2016 from University of Tsukuba. He is currently a master's program student at the department of chemistry, graduate school of science, Hiroshima University, under the supervision of professor Manabu Abe. His current research focuses on steric effect on the reactivity of singlet 2,2-dialkoxy-1,3-diyls. AbstractChemical bonding systems determine the nature of molecules. In organic chemistry, there are two bonding types for carbon carbon connections: σ-bonding and π-bonding. In this Highlight Review, several aspects of studies in the last two decades addressing a naive question "Is π-single bonding (CπC) possible?" were reviewed: (1) features of π-single bonded species; (2) molecular design for π-single bonding; (3) generation and detection of singlet diradicaloids with a π-single bonding character; (4) future prospects of π-single bonded species.

Extremely Long Lived Localized Singlet Diradicals in a Macrocyclic Structure: A Case Study on the Stretch Effect

“…The absorption maximum of localized singlet diradicals DR2 typically occur at about 500–600 nm . The absorption band corresponds to a π‐to‐π* electronic transition of the π–single bonding system (C‐π‐C) . All the experimental evidence suggests that the transient species at 580 nm is the singlet diradical S‐ DR2 g .…”

“…[11] The absorption band corresponds to a p-to-p*e lectronic transition of the p-single bonding system (C-p-C). [18] All the experimental evidences uggests that the transient species at 580 nm is the singlet diradical S-DR2 g.T he lifetimeo fS -DR2 g ( % 14 msa t2 93 K) was almost two-orders of magnitude longert han that of parent compound S-DR2 e (209 ns at 293 K). [14] As expected owing to the stretch effect induced by the macrocyclic system (Figure 2), S-DR2 g is highly kinetically stabilized as an extremely long lived localized singlet diradical.…”

Silicon–silicon π single bond

“…Such studies are now in progress. 2128.3 (1) 126.4(1) 121.9(2) θ 3 /°128.07 (2) 128.3 (1) 126.3(1) 121.9(2) θ 4 /°76. 35(4) 86.4 (1) 86.83 389.44 (8) X-ray crystallographic analysis.…”

“…1a). This new π single bond has recently been reported to present in singlet diradicals with π single bond character and stabilization of such singlet diradicals have been challenged [1][2][3] . On the other hand, studies on singlet diradicals consisting of heteroatoms have recently been developed [4][5][6] .…”

Bulky Substituent Effect on Reactivity of Localized Singlet Cyclopentane‐1,3‐diyls with π‐Single Bonding (C‐π‐C) Character

“…Radical-radical couplingr eaction [12][13][14] is an important fundamental reaction, involved in processes such as termination of radicalp olymerization [15][16][17] and deactivation of open-shell species. [18][19][20] Therefore, it is important to understand how the coupling reactionisinfluenced by steric effects in order to develop new organic materials with open-shell characters.…”